Telephone system



Feb. 1 s. E. PETERSON ETAL ,3 4

TELEPHONE SYSTEM Filed Aug. 2 1940 14 Sheets-Sheet 2 om-7 07b)" Suu'zch81 FH C270) C27] T'mm I E E putpr eni J C R250 R260 G292 INVENTORS .SelhE Pelerson Morris E Griffins ATTORNEYS s. E. PETERSON ETAL 2,311,774

TELEPHONE SYSTEM Feb. 23, 1943.

Filed Aug. 2, 1940 14 Sheets-Sheet 5 ORS Sel'h E Peferson Morris E Griffms ATTORNEYS A Con/motor SluLlch 31 {/49/ 1943! 5. E, PETERSON arm.2,311,774

I TELEPHQNE SYSTEM 1 Filed Aug 2; 1940 14 Sheets-Sheet 4 Fig.4

Morris E Griffins BY Y ' ATTORNEYS 70 Sezh E. Peterso'fi I Feb. 23,1943. s, PETERSON r 2,311,774

TELEPHONE SYSTEM Filed Aug. 2, 1940 14 Sheets-Shet 5 Trunk Operal'orFz'nder Bank ATTORNEYS CircuzT Mon 36 I '54 EIQ/mnge 5 14 Sheets-Sheet 6s. E. PETERSON arm.

TELEPHONE SYSTEM Fi1ed Aug. 2, 1940 Feb. 23, 1943.

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TELEPHONE SYSTEM Filed Aug. 2, 1940 14 Sheets-Sheet 8 mm o $25 EmConnecfor Switch .5!

Gaih onfrol Cl): 32

lNVEN TORS Seth E. PeTerson orrl's E. Griffins Feb.2 s,1943- s. E. PETERON HAL 2,311 114 TELEPHONE SYSTEM Filed Aug. 2, 1940 14 sheets-sheet 1oPepeazer Control Circuit 41 I (7/062 /o a/ aaf'lmoao f/08/ 028 Mb- 022/08 0/02? /0// i I R/O/O /002 Seth E. .5077

. Q Magi; E Griffins ATTORNEYS 23, 1943'v s. E. PETERSON ETAL ,3 4

TELEPHONE. SYSTEM Filed Aug. 2, 1940' 14 Sheets-Sheet 11 INVENTORS ISeth E.. Peferson 1943- s. E. PETERSON EI'AL 74 I TELEPHONE SYSTEM FiledAug. 2, 1940 4 l4 Sheets-SIIeet M 57/55 c//54, JOY/60 Gain Conzrolkleczor 44 lddl. Mal Lam MZI T i 5 bflmic/ml (ll/80% qua/1} 67/8213;was? 01/34 01/637 fizz 1*"7472 1 /7222 T7532 T7142 I 14/3, MOZV V V/ 423/4413 1 F /4/4T' 0/460; jg /45 4/ rma/7 t 405 T 614627 FIG 2 FIG 3 FIG 4FIG I me a FIG 7 FIG 8 Fly. 15 FIG 9 FIG 10 FIG I: V

FIG l2 FIG I3 FIG 14 myENToRS 861/) E. Pelensan Ag/grrzis E Gri/fins f vF I I) f i- 4 4 ATTORNEYS.

Patented Feb. 23, 1943 UNITED STATES PATENT OFFICE Riverside, 111.,assignors to Associated Electric Laboratories, Inc., Chicago, 11]., acorporation of Delaware Application August 2, 1940, Serial No. 349,928

84 Claims.

The present invention relates to telephone systems and more particularlyto improvements in automatic switching apparatus and-voice currentrepeating equipment of a character adapted for use in an exchange of theautomatic type.

In certain areas, such, for example, as small communities having alimited number oftele phone subscribers, it is desirable to provideexchanges of the unattended automatic type in order to provide highclass service and tominimize operating and maintenance costs. 'Insuchareas, subscriber lines frequently have widely different signal currenttransmission characteristics due to the variations in line length, thecondition of the lines, etc. Accordingly, the transmission eflicienciesof difierent connections involving different subscriber lines may varywidely depending upon the signal transmission characteristics and moreparticularly the signalcurrent losses. of the connected lines, withtheresult that, in certain instances, such, for example, as when twoextremely long lines are connected, the speech reproduction at thecalling and called substations may be practically unintelligible.

It is an object of the presentinvention, there-- fore, to provide, in atelephone system, apparatus for enhancing and maintaining more nearlyuniform the transmission efficiencies of connections involving lineshaving widely different signal current transmission characteristics.

It is another object of the invention to provide improved apparatus ofthe character described wherein the transmisssion efliciencycontrolequipment, when required, is automatically inserted in eachconnection incident to the setting up of the connection.

It is a further object of the invention taprovide, in an automatictelephone system, improved apparatus of the character described whereinvoice current repeaters common to the individualswitches of theautomatic switching equipment connections are routed.

It is another object of the-invention toprovide, for use in anarrangement of the character described, improved finder apparatus whichfunc-- tions operatively to associate the allotted-repeaters with theswitch trains to which the repeaters are respectivel assigned.

It is another object of the invention-to provide, in an arrangement ofthe character described, improved apparatus for automaticallymaintaining the balance of the voice current repeaters in use regardlessof the impedance char! acteristics of the lines with which the repeatersare associated, thereby to minimize singing in the repeater networks.

It is a further object of the invention to provide an arrangement of thecharacter described wherein the repeater balancing networks are,individual to the lines of the system and the balancing networks of anytwo connected lines are automatically selected and automaticallyconnected to the hybrid systems of the repeater serving the twoconnected lines incident to the setting upof the connection between thetwo lines.-

It'is another object ofthe invention to provide a telephone systemwherein the; lines extending to an exchange'are classified according to"the signal current transmission characteristics thereof and provisionsaremadefor auto matically raising the signal transmission level over anestablished connection by any one of several predeterminedaccounts, theparticular amount-beingdetermined by the total signalcurrentloss of theconnection-asindicatedby the class or classes in'which the calling andcalled lines of the connection, are respectivelyincluded.

It is another object of the invention to pro- Vide apparatus'of thecharacter described wherein provisions are madefor automaticallydetermining the gain of each assigned repeaterjjn accordancewiththetransmission elficiency classification of the-calling andcalledlines'served by the repeater, incident tothe setting'up'of theconnection i i-which therepeater is'includedr- It isafurther object ofthe inventionto-provide, for use in an arrangement I of the characterdescribed, improved finder apparatus which performs the dual function ofoperatively associat-' ing the allotted repeaters "with the j switchtrains to which the repeatersare assigned andof selectingthe-transmission efficiency classes in which the calling and calledlinesof the connectionsare included. 7

It is still another Qbject oi the invention toprovide anarrang-ement ofthe-character described wherein provisionsare made for automaticallyexcluding arepeater included in; acompleted connectionfrom'theconnection when theconnection is releasedat either the calling" orthecalled endthereof.

It is a still further object-of; theinventiorrto providein atelephonesystem ofthe, character described, an improved arrangementwherein the same circuit paths are utilized for line classificationtesting purposes and for distinguishing between calling lines of theloop circuit control type and calling lines of the simplex type.

The invention is illustrated in its embodiment in the automaticswitching equipment provided in a small automatic exchange of the typecommonly referred to as a community automatic exchange or C. A. X. Theautomatic switching equipment provided in the exchange comprises aplurality of finder-connector links, a link distributor, and the usualcommon equipment provided for ringing, supervisory and other signalingpurposes. The signal current losses of the lines extending to theexchange are widely different in character, and, in order to provide forimprovement in the signal transmission efficiency of connectionsinvolving the lines having transmission characteristics falling incertain classes, a plurality of voice current repeaters are provided.These repeaters are common to the finder-connector links of the exchangeand each thereof includes two hybrid systems, one system correspondingto the calling end of a connection and the other hybrid corresponding tothe called end of a connection. In order to insure the proper balance ofthe hybrid systems forming a part of a repeater included in a connectionset up between two lines, each of the'lines extending to the exchange isterminated in a line circuit which includes a balancing network havingimpedance characteristics designed to balance the impedancecharacteristics of the associated line.

An allotter common to the finder-connector links of the exchange isprovided for assigning the voic current repeaters to the use of thelinks in a predetermined order. For the purpose of operativelyassociating an allotted or assigned repeater with the link to which itis assigned, link finder apparatus is provided. This apparatus alsoperforms the function of determining the transmission efliciency zonesor classes in which the calling and called lines of a connection routedthrough one of the links are included. More specifically, this finderapparatus is of the allrelay type, the test or counting relays thereofoperating through a first cycle to select the link with which aparticular assigned repeater is to be associated and through a secondcycle to determine the transmission efficiency classes of the callingand called lines involved in the connection routed through the selectedlink. This second cycle of operation of the finder relays is alsoutilized to determine whether or not the transmission efficiencycharacteristics of the calling and called lines are such that a repeateris not required in the connection therebetween for satisfactory signalcurrent transmission thereover. Apparatus controlled in accordance withthe operation of the test or counting relays is provided for determiningthe gain of the repeater which is to be included in the particularconnection. The setting of this gain control apparatus is determined bythe transmission efiiciency classification of the calling and calledlines included in the connection. After this setting is determined, itis not changed. Moreover, the common equipment including the link finderapparatus is released following the operation of the gain controlapparatus. Auxiliary relay equipment is provided in each of the linksfor so controlling the repeater connecting equipment that, when aconnection is released at either the calling or called end thereof, therepeater included in the connection is eifectively excluded therefrom,thus prewith a second subscriber line.

venting the repeater from howling or singing to create a disturbance onthe connection. The arrangement of this auxiliary relay equipment isalso such that the repeater assigned to the connection is only includedtherein when the call is answered at the called substation.

Further features of the invention relate to the particular arrangementofthe finder-connector links, the repeaters and the control circuitsassociated therewith, whereby the above-outlined and additional objectsare attained.

The novel features believed to be characteristic of the invention areset forth with particularity in the appended claims. The invention, bothas to its organization and method of operation, together with furtherobjects and advantages thereof, will best be understood by reference tothe specification taken in connection with the accompanying drawings, inwhich Figures 1 to 14, inclusive, when combined in the manner shown inFig. 15, illustrate an automatic telephone system having incorporatedtherein the features of the invention briefly outlined above. Morespecifically, Fig. 1 illustrates one of the lines terminating at thecommunity exchange, the line circuit associated with this line, thefinder switch included in one of the finder-connector links, and thedistributor common to the several links; Figs. 2, 3, 4, 6, '7 and 8illustrate the details of the connector switch which operates inconjunction with the finder switch illustrated in Fig. 1 to form one ofthe finder-connector links; and Fig. 5 illustrates the line equipmentassociated with one of the inter-ofiice trunks to which the finder andconnector switches of the exchange have access, and the line equipmentassociated One of the voice current repeaters is illustrated in Fig. 7of the drawings. The gain control network for this repeater isillustrated in Fig. 8 of the drawings.

The control equipment associated with the voice current repeaters isillustrated in Figs. 9 to 14, inclusive, of the drawings. Morespecifically, in Fig. 9 there is shown a repeater allotter circuit, inFigs. 12 and 13 the link and line class finder apparatus is illustrated,and in Figs. 10, 11 and 14 the control equipment individual to therepeater shown in Fig. 7 is illustrated.

Referring now more particularly to the drawings, the system thereillustrated comprises a C. A. X. at which are terminated a plurality ofsubscriber lines including the lines 9 and II and a group of ring-downtrunks including the trunk 54I extending to a distant exchange 5 of themanual type. The subscriber lines terminating at the C. A. X. may be ofthe single party or multiparty type, the line I I being illustrated as asingle party line extending to the substation A and the line 9 beingillustrated as a multiparty line serving both the substations B and C.Each subscriber line terminates in the exchange in a line circuitindividual thereto. Thus, the line II extends to a line circuit I0 whichconventionally comprises a line relay RI 30, a cut-off relay RI 29 and aslowacting lockout relay RI ID. This line circuit also includes a linebalancing network individual to the line I I which comprises a resistor21 connected in series with a condenser 23. The resistance andcapacitance values of the two elements 21 and 23 are so proportionedthat the frequencyimpedance characteristic of the network approximatesthe frequency-impedance characteristic of the line II with theequipmentof the substation A connected to this line, at all frequencieswithin the audio range. In a similar manner,

the line Swhich serves the substations B and C is terminated in a linecircuit 34 which includes a line relay R533, a cut-ofi relay R525, aslowacting lockout relay R5|0 and a balancing network comprising theseries connected resistor 54! and condenser 546. This network, like thecorresponding network included in the line circuit I5, is characterizedby a frequency-impedance characteristic which approximates thefrequency-impedance characteristic of the line 3 with the substationequipment of either of the two substations B and connected to this line,at all frequencies within the'audio range. Th trunk 54| interconnectingthe C. A. X. with the exchange terminates in the C. A. X. in a trunkcircuit 35 which may be of conventional arrangement.

As indicated above, the automatic switching equipment provided in the C.A. X. comprises a plurality of finder-connector links of which only thelink comprising the finder switch 25 and the connector switch 3| hasbeen illustrated. For the purpose of assigning these links to the use ofcalling lines in a predetermined order, there is provided a linkdistributor 25 which may be of any desired construction and arrangementalthough preferably is of the type embodying a ro tary switch for linkselecting purposes. The con nection and arrangement of the severalfinderconnector links provided in the C. A. X. are identical. Further,the finder switches may be of substantially conventional form.Accordingly, the finder switch 23 has, for the most part, been onlyschematically illustrated. It is noted, however, that this finder switchis equipped with an extra bank of contacts and an extra pair of wipers565 and |56 which, in cooperation with the contact sets of the extracontact bank, are utilized for the purpose of associating the hybridbalancing networks individual to the various lines with the voicecurrent repeater equipment. In order to facilitate the explanation ofthe operation of the finder switch 23, the switch-through relay R|35 andthe finder start relay Rid-ll, both of which are conventionally embodiedin finder switches of all types, have been illustrated in the drawings.The control circuits for these relays have, however, been omitted inorder to shorten the explanation of the operation of the system. The

finder switches individual to the various links are arranged to controla repeater start relay R|5J which is provided for the purpose ofcontrolling certain of the repeater control circuits referred to morespecifically hereinafter.

The connector switch 3|, like the finder switch 25, is of the well-knownStrowger type and is universal in character in that it includesprovisions for automatic trunk selection, automatic ringing on selectedtrunks of the ring-down variety, selective code ringing of substationsserved by multiparty lines, revertive call signaling by the directorynumber dialing method, and testing a called line to determine whetherthe line is arranged for simplex or loop control of the link and linecircuit equipment. More specifically, this connector switch comprises aStrowger switching mechanism, the wipers of which are first steppedvertically and are then rotated under the control of the vertical androtary magnets 433 and 402,

respectively, and are released under the control of a release magnet435. This switching mechanism also comprises three sets of verticaloffnormal springs 433, 4i i and 2 5, tenth step cam springs H3 and twosets of normal post springs 433' and 405', the purpose of which isexplained inthe following portion'of the specif cation. For the purposeof selecting the code" of the" ringing current which is to betransmitted over' a line seized through the outlet contacts of' theconhector switch 3|, there is provided" in this switch a ringing codeselector 33. This selectoris" in the form of a rotary switch of thewell-known minor type which comprises two sets of contacts 860 and 362two wipers and 86 3, an operating magnet 865 for driving the wipers overthe contacts of their associated contact sets, a release magnet 864 andaset of ofi-normal springs 365 which are operated into engagement whenthe two wipers 85| and 853 are moved from the positions illustrated inthe drawings. In order to perform the circuit control operations necessary to the rendition of the services briefly outlinedabove, a pluralityof relays are provided in the connector switch 3|. More specifically,the relay equipment of thisswit-ch comprises a: pulsing relay R259, 2.slow-acting hold relay R269,- a pair of reverting call relays R255 andR4533, a called simplex line identification relay R245, a link releaserelay R220, and a paysta-tion tone repeating relay R233. This equipmentfurther comprises a hold slave relay R3), a lock pulse relay R325, acalling simplex line identification relay R330, a sloW-to-operate answerrelay 33%, a line relay R359, a pair of back-bridge relays R355 andR333, a pulse circuit transfer and supervisory relay R310, a slow-actingdigit relay R380, a busy test relay R3 33, a digit responsive transferrelay R4 H], a ring cut-off relay R320, a second slow-acting digit relayR443, a ringing relay R 255, a cutthrough relay R450, an automatic trunkhunting or cut-in relay R410 of the two-step type, a ring pickup relayR480 and a slow-to-operate cutthrough slave relay R490. There is furtherprovided in the connector switch 3| a group of auxiliary relays R103,R1) and R123, illustrated in Fig. '7 of the drawings, which function tocontrol the inclusion and exclusion of an assigned voice currentrepeater in a communication channel set up by way of this switch. Morespecifically, the link circuit is so arranged that an assigned voicecurrent repeater may be substituted for the repeating coil 650 in acommunication channel established by way of the link. The actual cut-inof the assigned repeater is under the control of a cut-in relay R635which, in turn, is arranged to be controlled by the ring cut-off relayR420 of the connector switch and certain of the relays embodied'in thecontrol circuit associated with the assigned repeater.

In the system arrangement illustrated provisions are made for using anyone of five voice current repeaters in conjunction with any one oftwelve finder-connector links. Each of these repeaters has individuallyassociated therewith a repeater control circuit and a gain controlnetwork. Thus, the repeater 45 is arranged to be controlled by arepeatercontrol circuit 4| which includes a gain control selector 44 forcontrolling the setting of a gain control network 32 which is providedto determine the gain of the amplifiers in the repeater 45. Morespecifically, the repeater 45 comprises an east-west amplifier 46, awest-east amplifier 43, and two terminal hybrid systems 41 and 48 whichrespectively correspond to the calling and called ends of an establishedconnection. The two amplifiers 46 and 49 are of the well-knownthermionic type, and the connection and arrangement of theseamplifierswith the terminal hybrid systems '41 and '48 and with the gaincontrol circuit 32'may be of any desired type well known in the art.Although not illustrated in the drawings, the repeater 45 is preferablyequipped with channel blocking and unblocking control means of thethermionic or loss type such that when the east-west channel amplifieris in use, the west-east channel amplifier 49 is blocked againstoperation, and vice versa. The gain control circuit 32 is divided intotwo sections 32a and 32b of identical circuit arrangement which arerespectively included in the signal current paths connecting the outputcircuits of the amplifiers 46 and 49 with the hybrid systems 4'1 and 48.Each of these sections is of the shunt-series resistance type, the shuntand series resistances included in the respective associated amplifieroutput paths being controlled by the setting of the relays R810, R020,R830, R840 and R850.

The control circuit 41 individual to the repeater 45 comprises a groupof twelve connect relays including the relays R1120, R1130 and R1140,which individually correspond to the twelve finder-connector links, anda group of auxiliary control relays. This latter group of relaysincludes a start relay R1000, a start slave relay R1010, a controlcircuit release relay R1020, a finder stop and circuit transfer relayR1030, an anode voltage control relay R1060, and a plurality of circuittransfer relays R1040, R1050, R1010, R1080 and R1100. The auxiliaryrelay equipment of the circuit 41 also includes a cut-in relay R1110 andthe previously mentioned gain control selector relays 44. The relays ofthe latter group, namely the relays R1400, R1410, R1420, R1430, R1440and R1450 individually correspond to the six classes of lines and, whenenergized alone in various combinations, function to determine thesetting of the relays in the gain control circuit 32. The sixth relay ofthe gain control selector group 44, namely, the relay R1450, whenoperated, indicates that the repeater 45 is not to be included in acommunication channel set up by way of the finder-connector link towhich it is assigned.

As indicated above, the various repeaters and their associated controlcircuits are allotted to the use of links assigned to the use of callinglines through operation of the repeater allotter circuit 40. Thiscircuit comprises a start relay R900 and a plurality of sloW-to-operateallotter relays R910, R920, R930, R940 and R950 which individuallycorrespond to the five repeaters available. This circuit also includes arepeater start relay R990, a reset relay R960 and an overflow relay R910which functions to control the all-busy meter 992 and associatedsignaling lamp 994 in a manner such that these elements are energizedwhen all of the repeaters are busy. The equipment common to therepeaters and their associated control circuits also includes a timepulse relay R980 which functions automatically to initiate the releaseof an assigned repeater control circuit in the event the circuit isdefective.

The equipment common to the repeaters and their respective associatedcontrol circuits also includes the link and line class finder apparatus42, illustrated in Figs. 12 and 13 of the drawings. As indicated above,this apparatus performs two functions, namely that of finding the linkwith which an assigned repeater is to be associated and that ofdetermining the classification of the calling and called lines of theconnection. Briefly described, this apparatus comprises twelve countingor test relays R1200 to R1210,.inclusive,

and R1310 to R1340, inclusive, a start relay R1350 and a pair of pulsecontrol relays R1360 and R1310, the first of which is of the slow-actingtype.

In addition to the equipment briefly described above, there is providedin the C. A. X. the usual auxiliary equipment comprising ringing voltageand tone voltage generating equipment, a ringing code interrupter, andsuitable supervisory apparatus. This common equipment also includes atiming device 30 which is provided for the purpose of automaticallyreleasing links seized over lines having permanent calling conditionsthereon.

The operation of the system will best be understood by consideringspecific calls initiated on the lines terminating at the C. A. X, andpointing out the differences in the operation of the illustratedfinder-connector link and the associated repeater equipment incident tothe handling of the calls of different types.

ROUTING A CONNECTION TO THE CONNECTOR Swrrcn 31 Assuming that a call isinitiated at the sub station A, for example, the line relay R139 isenergized when the calling subscriber removes the receiver provided atthis substation from its supporting hook or cradle. The line 11extending to the substation A is illustrated as being provided forsimplex control of the link and line circuit equipment and, accordingly,the operating circuit for the relay R130 may be traced as extending fromground through the hook switch provided at the substation A, over thetwo line conductors C191 and C102, through the contacts 121 and 122, andthe upper and lower windings of R139 to battery. When thus energized,the relay R130 operates to complete, at its contacts 131, a pathincluding the contacts 111 for impressing negative battery potentialupon the marking lead C104, thereby to mark the line 11 as a callingline in the bank contacts of the various finder switches and to preparea circuit for energizing the cut-off relay R when the finder switch ofan assigned link operates to switch the line I 1. At its contacts 133,the relay R opens a point in an alternative circuit for energizing thecut-off relay R120. At its contacts 132, the relay R139 completes anobvious path for impressing ground potential upon the private conductor010i, thereby to mark the line 11 as busy in the bank contacts of theconnector switches having access thereto. At its contacts 134, the relayR139 completes a path including the contacts 112 for impressing groundpotential upon the distributor start lead C22.

When the lead C22 is connected to ground, the control equipment of thedistributor 25 operates in a well-known manner to complete circuits forinitiating the operation of the finder switch of a previously selectedlink. Assuming that the finder-connector link illustrated is assigned tothe use of the line 1 1, the control equipment of the distributor 25,upon operating, completes a circuit for energizing the finder startrelay R140, and a circuit for energizing the vertical magnet of theStrowger switching mechanism included in the finder switch 29. Thisvertical magnet, operating in conjunction with the pulsing relayconventionally embodied in the distributor 25, functions to elevate thewipers 161 to 168 of the finder switch 20 to a position opposite thelevel of bank contacts at which the conductors of the line 11 areterminated. This level is marked through the application of groundpotential to the distributor start conductor C22, so that, when theWipers of the finder switch 20 are elevated to .a position opposite thiscontact level, the vertical movement thereof is arrested and a circuittransfer'opera'tion is eiiected, whereby the pulsing relay of thedistributor 25 operates to transmit current pulses to the rotary magnetof the Strowger switching mechanism. This magnet functions to rotate thewipers I! to I66, inclusive, until they are operated into engagementwith the contacts terminating the conductors of the line II. At thistime, a circult is completed for energizing the upper or operatingwinding of the finder switch-through relay R135 in series with thewinding of the cut-off relay RI20, this circuit extending from groundthrough the operated contacts of certain of the relays embodied in thedistributor 25, the upper or operating winding of 'RI35, the wiper I84,the marking lead CI04, the contacts I3I and III, and the winding of RI20to battery. When its upper winding is energized over this circuit, thefinder switch-through relay RI35 operates to close its contacts I33,I31, I38 and I39, thus extending the calling line to the connectorportion of the link. In operating, the relay RI 35 also completes alocking circuit for itself, which circuit includes its lower or holdingwinding and the winding of the rotary magnet of the Strowger switchingmechanism embodied in the finder switch 20. At its contacts I39, therelay RI35 completes a path including the grounded control conductorCI1iI for impressing ground potential directly upon the marking leadCI04, this path being'prepared in response to the operation of the lineand hold relays embodied in the connector switch 3|, in the mannerexplained hereinafter. When the lead CI04 is grounded, the cut-off relayRI20 is energized over an obvious circuit. In operating, the relay RI20first locks to the grounded lead CI04 through its preliminary makecontacts I23. After this locking circuit is completed, the relay RI20opens its contacts I2I and I22 to disconnect the windings of the linerelay RI30 from the conductors CIOI and C'I'02 of the line II, therebyto deenergize the line relay and to clear the line I I of the impedancerepresented by the windings of this relay. At its contacts I25, therelay RI20 opens a point in the resistance path normally shortcircuitingits own winding. At its contacts I24, the relay R120 completes a pathfor impressing paystation tone voltage upon the control conduc tor CI'IIof the link circuit in the event the line II is of the paystation type.In this regard it will be understood that the paystation tonetransmission circuit comprising the condenser I24 and the contacts I24is only provided in the line circuits terminating lines of thepaystation variety. At its contacts I21, the relay RI20 opens a point inthe path provided for impressing ground potential upon the permanentsupervisory lead CISI. At its contacts I23, the relay Ri20 completes acircuit for energizing the slow-acting line lockout relay R5 I 0.

The relay RI30, upon restoring in response to the operation of thecut-01f relay R120, opens its contacts I31 to interrupt the initiallycompleted operating circuit for the cut-ofi relay RI'20, opens itscontacts I32, and closes its contacts I33 to complete an alternativepath for impressing ground potential upon the private conductor C101 ofthe line II. This alternative path extends from the grounded controlconductor CI1I by way of the contacts I39, the wiper I64, C104 and thecontacts I23 and I33 to the private conductor CI01. At its contacts I34,the relay RI30 opens a point in the prepared locking circuit for thelookout relay RIM and disconnects the distributor start lead C22 fromground. When this lead is disconnected from ground, the distributor 25operates in the usual manner to select another idle link for use inhandling the call next initiated on one of the lines terminating at theC. A. X.

The lockout relay RI I0, upon operating, closes its contacts II3 toprepare a locking circuit for itself, and closes its contacts M4 toprepare the above-mentioned path for impressing ground potential uponthe permanent supervisory lead OI8I. At its contacts II2, the relay RII0 opens another point in the above-traced path for impressing groundpotential upon the distributor start lead C22. At its contacts III, therelay RIIO opens another point in the above-traced line marking path andthe initially completed circuit for energizing the cut-off relay RI20.At its contacts H6, the relay RII3 disconnects the extra control leadCI03 from ground. At its contacts N5, the relay RI I0 prepares a pathfor energizing one of the line classification relays included in thegain selector of the repeater control circuit associated with anassigned repeater, all in the manner explained more fully hereinafter.

When the finder start relay Rhiil operates in the manner pointed outabove, it completes a circuit for energizing the relays R250 and R350 inseries, this circuit extending from ground by way of the winding ofR350, CI12, the contacts I41, CI14, the contacts 636, the repeating coilwinding 602, C209, the contacts 2%, C295, the contacts 345, C294 and thewinding of R250 to battery. When thus energized, the relays R250 andR350 both operate. Upon operating, the relay R250 completes a circuitfor energizing the lock-pulse relay R320, this circuit extending fromground by way of the contacts 313, C211, the contacts 253, C213 and thewinding of R320 to battery. At its contacts 25I, the relay R250 opens apoint in a priming circuit for itself. At its contacts 252, the relayR250 prepares a holding circuit for the slow-acting hold relay R260.

The relay R320, upon operating, completes the prepared operating circuitfor the hold relay R260, this circuit extending from ground by way ofthe contacts 224, C215, the contacts 32I, C215 and the winding of R250to battery. At its contacts 322, the relay R320 opens a point in thecommon portion of the circuits over which current pulses are transmittedto the vertical and rotary magnets 400 and 405, the relay R380 and theoperating magnet 865 of the ringing code selector switch 33. At itscontacts 323, the relay R320 completes a locking circuit for itself,this circuit extending from ground by way of the resistor 326, thecontacts 323, C211, the contacts 253, C218 and the winding of R320 tobattery. At its contacts 324, the relay R320 prepares a circuit forenergizing the transfer and supervisory relay R310. At its contacts 325,the relay R320 opens a point in one of the circuits for energizing thereverting call relay R430.

The hold relay R260, upon operating, completes, at its contacts 264, theabove-mentioned path for impressing ground potential upon the controlconductor CI1I, this path including the conductor C281 and the contacts358. At its contacts 205, the relay R260 opens a point in the operatingcircuit for the relay R240; At its contacts 263, the relay R260 furtherprepares the above-mentioned priming circuit for the pulsing relay R250.At its contacts 26|, the relay R260 prepares the operating circuit forthe link release relay R220. At its contacts 262, the relay R260prepares a test circuit, including the upper winding of the cut-in relayR460, for energizing this relay in the event the line subsequentlyselected is idle.

When ground potential is impressed upon the conductor C281 by the holdrelay R260, the hold slave relay R3l0 is energized over a circuitincluding this conductor, the contacts 245 and the conductor C288. Uponoperating, the relay R3l0 closes its contacts 3|2 to prepare theabovementioned circuit for transmitting repeated dial pulses to thethree magnets 400, 402 and 865, and to the digit transfer relay R380. Atthe contacts 3|2, the relay. R3l0 also completes a multiple circuit forenergizing the hold relay R260, this circuit extending from ground byway of the contacts 224, C215, the contacts 3I2, C216, the contacts 252and the winding of R260 to battery. At its contacts 3|6, the relay R3l0prepares the incomplete operating circuit for the slow-toreleasereverting call relay R430. At its contacts 3", the relay R3|0 opens apoint in the common portion of the operating circuits for the tworelease magnets 405 and 864. At its contacts 3|5, the relay R3l0completes an obvious path for impressing ground potential upon therelease conductor C286. At its contacts 3|3, the relay R3l0 opens theabove-traced operating circuit for the lock-pulse relay R320. At itscontacts 3| the relay R3 prepares the operating circuit for theslow-to-operate control relay R340. At its contacts 3|4, the relay R3l0prepares the operating circuit for the reverting call relay R240.

When ground potential is impressed upon the release conductor C286 bythe hold slave relay R3| 0, the lower winding of the called simplexrelay R2|0 is energized over a circuit including this conductor and theresistor 2 I 6, and the lower winding of the calling simplex relay R330is energized over a circuit including this conductor and the resistor332. These two relays, when thus energized over circuits including theresistors 2|6 and 332', respectively, do not operate but are renderedexceedingly fast to operate in the event the upper windings thereof aresubsequently energized. y,

When ground potential is impressed upon the release conductor C286 bythe hold slave relay R3l0, a circuit including this conductor and theoff-normal springs 4| l' is completed for energizing the transfer relayR4 I 0. Upon operating, the relay R4|0 closes its contacts M6 to preparea locking circuit for itself, and closes its contacts M2 to prepare thecircuit for transmitting repeated dial pulses to the vertical magnet400. At its contacts 4| the relay R4|0 opens a point in the commonportion of the circuits for transmitting repeated dial pulses to therotary magnet 402 and the operating magnet 865 of the ringing codeselector switch 33. At its contacts M5, the relay RM 0 opens a point inthe operating circuit for the relay R440. At its contacts M4, the relayR4|0 opens a point in the circuit for energizing the rotary magnet 402during a trunk-hunting operation on the part of the connector switch3l.At its contacts 4 l3, the relay R4|0 prepares one of the operatingcircuits for the ringing relay R450. At its contacts 4|1, the relay R4|0completes a path for impressing dial tone voltage upon the calling endof the connection, this path extending from one terminal of the dialtone current source, not shown, by way of the contacts 4|1 and 448,C555, and the condenser 555' to the talking conductor C291. From thispoint the dial tone current is transmitted out over the calling line andover a return circuit which terminates at the opposite terminal of thedial tone current source in the usual manner. The dial tone signalcurrent traversing the calling line, when reproduced by the receiverprovided at the calling substation A, indicates to the callingsubscriber that the dialing operation may be started.

As indicated above, the relay R350 is energized in series with thepulsing relay R250 when the finder start relay R|40 operates. Inoperating, the relay R350 completes a circuit for energizing the upperWinding of the calling simplex relay R330 in the event the calling lineis of the simplex type. In the present case, wherein the line H isarranged for simplex control of the line and link circuits, the upperwinding of the relay R330 is energized over a circuit which extends fromground by way of the contacts 6, the extra control conductor C|03, thewiper I63, the contacts I38, Cl15, the vertical off-normal springs 2| 5,C280, the contacts 33|, the upper Winding of R330, the resistor 33| andthe contacts 35| to battery. When this circuit is completed, the relayR330 closes only the prelimi nary make contacts 332 controlled thereby.Thereafter, and when the hold slave relay R3l0 operates to impressground potential upon the release conductor 0286, the lower winding ofthe calling simplex relay R330 is directly energized over a circuitincluding the contacts 332. The relay R330 now completes its operation,At its contacts 33|, the relay R330 interrupts its operating circuit astraced above. At its contacts 334, the relay R330 disconnects thepositive talking conductor C|13 of the link circuit from the groundedresistor 4|1'. At its contacts 333, the relay R330 completes a simplexpulsing circuit which extends from the substation A through the windingof the pulsing relay R250. One branch of this circuit may be traced asextending from ground by way of the springs of the hook switch at thesubstation A, C|0|, the wiper l6|, the contacts |36, C|13, the contacts632, the

repeating coil winding 60l, C650, the contacts 241, C296, the contacts341 and 333, C294 and the Winding of R250 to battery. The other branchof the simplex pulsing circuit extends from ground by way of the springsof the hook switch at the substation A, C|02, the wiper I62, thecontacts I31, C|14, the contacts 636, the repeating coil winding 602,C289, the contacts 246, C295, the contacts 345, C294 and the winding ofR250 to battery. The completion of this simplex circuit reduces byapproximately 50 percent the resistance of the circuit over which whichdial pulses are transmitted to the pulsing relay R250.

In the event the calling line is arranged for loop circuit control ofthe line relay embodied in its terminating line circuit, the linecircuit arrangement illustrated in Fig. 5 of the drawings will be used.It will be noted that in this line circuit the lookout relay R5|0 is notequipped with a set of break contacts through which ground potential isnormally impressed upon the extra control conductor C535. Accordingly,if the finder switch 20, for example, operates to seize the line 9through the line circuit 34, the circuit for energizing the callingsimplex relay

